I’ve looked at the NFL Draft a lot since starting this
blog. As the draft was here in Chicago this year, I found myself running into a
number of jerseys on the street when I went out for lunch on Thursday and
Friday. Even more surprising than the fact that people had travelled – in some
cases from pretty far away according to the jerseys – was the fact that a lot
of them were wearing jerseys of players who were disappointments if not outright busts. It
got me thinking about sunk costs and whether teams are any better than their
fans about cutting their losses.
To try to get at this we’ll need to know how much teams
value their draft picks – conveniently we do know this via the Jimmy
Johnson-popularized draft value chart – and then compare this to how much those
players are used. Usage is a bit tricky but I’m going to approximate it with
games started (1 full game) plus games played (2014 avg snaps non-starter /
2014 avg snaps starter, by position).
Before even getting to questions of usage, there is a
significant disparity in the proportion of players from each round who end up
making a roster.
|
Round
|
%
on Roster Year 1
|
|
1
|
97%
|
|
2
|
94%
|
|
3
|
83%
|
|
4
|
81%
|
|
5
|
70%
|
|
6
|
62%
|
|
7
|
52%
|
I am guessing that most of this comes down to talent
disparity, but there is certainly some aspect of sunk cost at work here. Lots
of later round picks – to say nothing of undrafted players – never make it onto
a roster to get into the rest of this analysis. They are, however, not the
topic of this analysis. I want to see if a player’s draft value still impacts
playing time even after making a roster.
The first cut of this is simply to look at draft weight
and usage, checking how much the former impacts the latter. The regressions for
each of a player’s first 6 seasons are below:
|
Usage vs Draft Weight
|
||||
|
|
|
|
Draft Weight
|
|
|
Year
|
R^2
|
Intercept
|
Coefficient
|
P-Value
|
|
1
|
0.22
|
4.53
|
15.87
|
0.00
|
|
2
|
0.16
|
6.88
|
13.87
|
0.00
|
|
3
|
0.10
|
8.10
|
10.71
|
0.00
|
|
4
|
0.08
|
8.84
|
9.18
|
0.00
|
|
5
|
0.05
|
9.49
|
6.58
|
0.00
|
|
6
|
0.04
|
9.88
|
6.14
|
0.00
|
The draft weight is a significant variable throughout the
first 6 years of a player’s career, but the strength of that relationship
declines over time. The 1st year model explains 22% of the variation
in usage while the 6th year model explains just 4%.